Criteria for Export Date (Supply Timing) in Intermediary Trade (Triangular Trade)

I am engaged in intermediary trade (triangular trade), where goods are imported from a third country and then re-exported to another country. I am wondering when I should determine the sales date (export date) for the purpose of recording sales slips and applying sales exchange rates. If the invoice date and the air shipment date (B/L date) are the same, there is no issue, but if they are different, which date serves as the standard? (Example: Goods are picked up from the importer on the invoice date, arrive at the airport the next day, and are then loaded onto the export flight.) The import terms are EXW, and the export terms are CIF.